Charged particle beam apparatuses, such as electron beam apparatuses have many functions in a plurality of industrial fields, including, but not limited to, inspection of semiconductor devices during manufacturing, exposure systems for lithography, detecting devices and testing systems.
Charged particle beams, e.g. electron beams are often used for micrometer and nanometer scale process control, inspection or structuring, wherein the charged particles are generated and focused in charged particle beam devices, such as electron microscopes or electron beam pattern generators. Charged particle beams offer superior spatial resolution compared to, e.g. photon beams due to their short wavelengths.
For instance, scanning electron microscopes (SEM) are used for many applications for high resolution surface imaging. In particular, low voltage SEMs with electron beam energies of 50 eV to 5 keV are widely used in applications where sample damage and sample charging should be avoided. Electron beam metrology and electron beam inspection are only a few application areas for semiconductor device manufacturing.
In general, mainly two basic requirements are to be considered for SEM columns. Firstly, the highest possible resolution should be achieved, which means a small spot size of the electron probe, preferably in the sub-nanometer range. Secondly, the highest possible probe current should be used in a given probe diameter. From this, two requirements for the design of the SEM optics result. The first requirement is a high brightness electron source. The second requirement is a low aberration objective lens for focusing the beam onto the sample, which means low chromatic aberration in the high resolution case, and low spherical aberration in mid-size, high current cases.
In view of the above, it is an object of the present invention to provide an electron beam system and optics for the electron beam system which provide a high brightness and a small virtual size, and, at the same time, low aberrations and good alignment of the electron beam in the electron beam system.